[Contrast echocardiography. Does it have a future?].

In the past thirty years echocardiography has revolutionized cardiologic investigation. The non-invasive access to anatomy, physiology, and heart diseases has become increasingly broader. Since the introduction of the M-mode technique and, progressively, of twodimensional echocardiography, Doppler, color flow mapping, transesophageal echocardiogram, and use of physical or pharmacologic stress, different methodologies have been added in pursuit of the optimization of cardiac assessment using ultrasound, and all of them have become consolidated in the clinical practice. Among the most recent techniques, real-time 3D echocardiography, assessment of ventricular function with tissue Doppler and strain-strain rate, and the use of contrast can be pointed out. Actually, the pursuit of contrast echocardiograms is not novel and has progressed slowly. In 1968, at the beginning of the history of echocardiography, in tests performed during cardiac catheterization, the injection of liquids in the cardiovascular system was observed to allow the formation of small bubbles that produced a cloud of echoes1. These bubbles, however, had large diameters in relation to the microcirculation, and could not pass through pulmonary capillaries, a fact that limited their use to a few clinical applications. In 1984, with the use of microbubbles with diameter lower than 10μ, the pulmonary capillary barrier was crossed and the left cavities could be opacifi ed with sonicated albumin2. In the 1990’s, countless studies on the development of contrast agents and technological advances in equipment were conducted, which made detailed assessments of the left cavities possible, and the expected investigation of the coronary artery circulation became closer to fullfi lment3-7. Research on contrast agents have aimed at obtaining an agent with microbubbles able to pass through capillaries with the least diameter possible, with a longlasting stability, acoustic impedance different from that of tissues, higher concentration, low toxicity, and rapid metabolism and excretion8. With these purposes, we can interfere with: (1) the size of the microbubbles, (2) the gas that fi lls them, and (3) the substance that forms their outer layer. As regards the size, microbubbles should be smaller than 10μ; however, within this range the largest bubbles are more stable. Gases are preferably heavy, inert and not very soluble, whereas albumin, phospholipid, carbohydrate, or biopolymer capsules enable a higher stabilization6,9. First-generation contrast agents are represented by AlbunexTM (air fi lled microbubbles and sonicated albumin in the outer layer), and by LevovistTM (air fi lled and galactose with traces of palmitic acid in the outer layer).